1. What is the structure and properties of an atom? An atom consists of a nucleus and a vast region of space outside the nucleus. Nucleus is dense. Electrons are present in the region of space outside the nucleus. They are negatively charged and weakly bound to the atom. Electrons are often removed from and added to an atom by normal everyday occurrences. The nucleus of the atom contains positively charged protons and neutral neutrons . Proton- in nucleus, tightly bound, positive charge, and massive. Neutron- in nucleus, tightly bound, no charge, and massive. Electron- outside nucleus, weakly bound, negative charge, not big. Ion- charged ion Anion- negative Cation- positive Electronegativity- how tight its bound.
2. What is the symbol and unit of electric charge? Kind of charge (Q, q) Unit of charge- Coulombs (C) e=-1.6 x 10 ^-19 C- charge in a single electron p=+1.6x 10 ^-19 C- charge in a single proton Units are usually μC and nC
3. Distinguish between positive and negative charges in as many ways as possible. Negative charges- -electrons - 9.11 x 10^-31 Kg -mobile Positive Charges- Ions- much bigger than single electrons - more than 10,000 times more massive than electron - immobile
Problems (1-4)
1. What is the charge on a rod that has 15 excess electrons? 2. What is the charge on a pith ball that has 3.15 x 1016 electrons? 3. How many electrons are missing from a balloon that has a charge of 4.19 x 10-5 C?
4. If a metal object receives a positive charge, does its mass increase, decrease, or stay the same? What happens to its mass if the object receives a negative charge? Losing electrons missing mass Mass increases when gaining electrons
Lesson 1 Summary 2A
What (specifically) did you read that you already understood well from our class discussion? Describe at least 2 items fully.
I understood the section on Charge as a Quantity which was very similar to the class discussion. It made sense in the reading that Coulumbs measures the amount of charge an object possesses.Under neutral vs charged objects I was able to make the idea of charged objects clearer in my head. Seeing them gain or lose electrons.
What (specifically) did you read that you were a little confused/unclear/shaky about from class, but the reading helped to clarify? Describe the misconception you were having as well as your new understanding.
What (specifically) did you read that you still don’t understand? Please word these in the form of a question.
What are the processes of polarization?Polarization- take something charged and touch something neutral. Pushes same charges (neg or pos) to opposite side. Does not change pos. or neg. count by causes a charge.
What (specifically) did you read that was not gone over during class today?
We really did not go over conductors and insulatorsInsulators dont allow electrons to move easily
Conductors allow electrons to move easily- mostly metals
Guiding Questions 4-9
4. Describe the properties of electric forces. Electric Force: non contact force Any object can exert this force Same laws apply to electric force as others Opposites attract and same repel
5. Distinguish between insulators and conductors. Conductors are materials that permit electrons to flow freely from atom to atom and molecule to molecule. Insulators are materials that impede the free flow of electrons from atom to atom and molecule to molecule. If charge is transferred to an insulator at a given location, the excess charge will remain at the initial location of charging. The particles of the insulator do not permit the free flow of electrons
6. What is polarization? Polarization is the process of separating opposite charges within an object. The positive charge becomes separated from the negative charge. By inducing the movement of electrons within an object, one side of the object is left with an excess of positive charge and the other side of the object is left with an excess of negative charge. Charge becomes separated into opposites. Process always involves the use of a charged object to induce electron movement
7. How does a neutral object acquire charge? A neutral object will acquire a charge by losing or adding protons
8. Distinguish between the 3 charging processes. Charging by friction: electron affinity- the property of electron affinity refers to the relative amount of love that a material has for electrons- willingness to add electrons- transferred electrons after being rubbed together. Charging by induction Charging by conduction- involves conduct
9. What is the law of electric charge? The interaction between charged objects is a non-contact force that acts over some distance of separation.
Methods of Charging
Polarization Conduction/ Contact- same charge as charging object after being touched by it. move over during polarization than electrons move once being touched. Induction- start out with a neutral object- bring over a negative rod to start- object becomes polarized- grounding sphere (attached to ground- aground) Electrons leave and go down to ground. When detach grounding wire object is positive Acquires opposite charge from charging object
Lesson 2 Summary 2A
1. What (specifically) did you read that you already understood well from our class discussion? Describe at least 2 items fully. Charging by friction made a lot of sense to me. Two objects are rubbed together and one has a greater attraction for electrons than the other. When they are rubbed, the one that has a greater attraction receives electrons from the other object. This object now has a negative charge with excess electrons. The other object lost a lot of electrons and now has a positive charge. I understood well how to charge by conduction using a negatively charged object. A negatively charged object makes contact with a neutral object. Since the electrons inside the negatively charged object repel, many of them flow into the neutrally charged object upon contact. This makes the once neutral object have a negative charge.
2. What (specifically) did you read that you were a little confused/unclear/shaky about from class, but the reading helped to clarify? Describe the misconception you were having as well as your new understanding. The grounding section was explained well. I understand now that when a person touches a charged object, the object becomes neutral.
3.What (specifically) did you read that you still don’t understand? Please word these in the form of a question. Whats pathway?
4. What (specifically) did you read that was not gone over during class today? We did not really go over charging by induction
Sticky Lab
Discussion Questions:
Explain how materials become charged through their interaction with one another.
In this case, when materials are rubbed against each other, electrons are shed. The object with a greater affinity for electrons will take the electrons that are shed by the other object. Now this object is negative and the other is positive.
Why, when you stroke a cat's fur, or comb your hair on a cold, dry day can you hear a crackling sound? Doing these things in a darkened room, you can actually see sparks. Explain.
This occurs because you are creating friction between your hand and a cat's fur. When this occurs, static electricity builds up and creates a positive charge on one object and a negative on the other. The sound and sparks that result from this are the electrons moving from the negative object to the positive one.
Photocopying machines use the principles of electric charges. Do research to find out how photocopying machines work. Be sure to list your sources.
Copy machines work by using a process known as xerography. They have a a special film known as a photoreceptor, which when charged, can erase a charge by shining light upon it. When copying, the machine's electricity causes the air to form positive charges, which are spread onto the photoreceptor. A beam of light is then used to write on the photoreceptor; the location of the writing depends on the original paper placed into the copier. Toner, which has a negative charge, is then shaken over the sheet and sticks to the positive charges left on the photoreceptor. The piece of paper is then pressed onto the photoreceptor, which, in turn, presses the content from the original piece of paper onto the copying paper.
Materials have a characteristic which evaluates their attraction for electrons. The Triboelectric Series orders materials by their affinity for gathering electrons through contact from other materials. The materials toward the top of the list are likely to give up electrons in these interactions whereas those at the bottom are more likely to gain electrons. Five materials are ranked as follows, with more positives meaning least desiring electrons.
Accepts Most Electrons to Gives away the most
1. Teflon
2. PVC
3. Polyester
4. Styrene
5. Wool
Determine the net charge on each item when the following pairs of materials are rubbed together. (In other words, which ends up giving up electrons and which ends up accepting them?)
PVC and Wool
PVC will accept from wool
PVC and Teflon
Teflon accepts electrons from the PVC
PVC and Polyester
PVC accepts the electrons of the Polyester
Teflon and Polyester
Teflon accepts the electrons of the Polyester
Styrene and Wool
Styrene accepts the electrons from the wool
Conclusion: Revisit your hypotheses and answer the objectives in light of your observations. Be sure to be specific, supporting your statements with evidence from the lab.
Practice Problems (5-7, 12)
12. Increasing speed
Balloon Activity
Electrostatic Force
The attraction or repulsion between 2 electric charges
Fe= (Ke|q1||q2|)/d^2
Charge is in C
Make sure not micro Coulombs
Distance in meters
Force in newtons
Exert equal and opposite forces on 1st.
Ke= 9x10^9 Nm^2/c^2
Electrostatic can attract and repel but gravitational can only attract
Putting two positively charged together you get increasing motion
Positive and Negative increasing motion
Lesson 3 Summary 2A
What (specifically) did you read that you already understood well from our class discussion? Describe at least 2 items fully.
I already understood that like charges repel and that opposite forces attract, and that when these interactions occur the objects exert an equal force on each other. I knew that this force can be measured in Newtons.
What (specifically) did you read that you were a little confused/unclear/shaky about from class, but the reading helped to clarify? Describe the misconception you were having as well as your new understanding.
I didn't fully understand that the relationship between electrostatic force and distance is inverse square. The reading really clarified that.
What (specifically) did you read that you still don’t understand? Please word these in the form of a question.
What are point charges?
What (specifically) did you read that was not gone over during class today?
We did not discuss when an object is considered to be in equilibrium.
Electric Fields
Lesson 4 Summary Method 1
Action at a distance The electric force acts over the distance separating the two objects. Electric force is an action-at-a-distance force. There are two categories of forces - contact forces and non-contact forces. The charged object affects other charged objects that were in the surrounding neighborhood. The best explanation to this question involves the introduction of the concept of electric field. The concept of a field force is utilized by scientists to explain this. While all masses attract when held some distance apart, charges can either repel or attract when held some distance apart. A charged object creates an electric field. A Van de Graaff generator is a large conducting sphere that acquires a charge as electrons are scuffed off of a rotating belt. The Van de Graaff generator is said to create an electric field in the space surrounding it. An electric charge creates an electric field and as masses get near it, it will have a stronger effect.
Electric Field Intensity
Electric field strength is a vector quantity; it has both magnitude and direction. The magnitude of the electric field strength is defined in terms of how it is measured.The strength of the source charge's electric field could be measured by any other charge placed somewhere in its surroundings. The charge that is used to measure the electric field strength is referred to as a test charge. The magnitude of the electric field is simply defined as the force per charge on the test charge. Since electric field is defined as a force per charge, the standard metric units are Newton/Coulomb or N/C. The electric field strength is not dependent upon the quantity of charge on the test charge. The electric field strength is not dependent upon the quantity of charge on the test charge. Coulomb's law states that the electric force between two charges is directly proportional to the product of their charges and inversely proportional to the square of the distance between their centers. E =F/q equation. The electric field strength is dependent upon the quantity of charge on the source charge (Q) and the distance of separation (d) from the source charge. The electric field strength formula illustrates an inverse square relationship between electric field strength and distance, known as an inverse square law. Electric field strength is location dependent, and its magnitude decreases as the distance from a location to the source increases. Every electric charge creates an electric field. The strength of a source charge's electric field is dependent upon how charged up the source charge is. The electric field equation shows that as you get closer and closer to the source of the field, the affect becomes greater and greater, the electric field strength increases. The magnitude of the electric field vector is calculated as the force per charge on any given test charge located within the electric field. The precise direction of the force is dependent upon whether the test charge and the source charge have the same type of charge. A positive test charge is pushed or pulled when in the presence of the electric field. Electric field vectors are always directed towards negatively charged objects.
Electric Field Lines Electric field lines point in the direction that a positive test charge would accelerate if placed upon the line. As such, the lines are directed away from positively charged source charges and toward negatively charged source charges. One common convention is to surround more charged objects by more lines. Objects with greater charge create stronger electric fields. Not only does the density of lines surrounding any given object reveal information about the quantity of charge on the source charge, the density of lines at a specific location in space reveals information about the strength of the field at that location. A second rule for drawing electric field lines involves drawing the lines of force perpendicular to the surfaces of objects at the locations where the lines connect to object's surfaces.A final rule for drawing electric field lines involves the intersection of lines. Electric field lines should never cross. Suppose that there are two positive charges - charge A (QA) and charge B (QB) - in a given region of space. Each charge creates its own electric field. Since electric field is a vector, the usual operations that apply to vectors can be applied to electric field. That is, they can be added in head-to-tail fashion to determine the resultant or net electric field vector at each location. Ultimately, the electric field lines surrounding the configuration of our two charges would begin to emerge. For the limited number of points selected in this location, the beginnings of the electric field line pattern can be seen.
Electric Fields and Conductors Electrostatic equilibrium is the condition established by charged conductors in which the excess charge has optimally distanced itself so as to reduce the total amount of repulsive forces. There is no further motion of charge about the surface after this equilibrium. One characteristic of a conductor at electrostatic equilibrium is that the electric field anywhere beneath the surface of a charged conductor is zero. If an electric field did exist beneath the surface of a conductor, then the electric field would exert a force on all electrons that were present there. This net force would begin to accelerate and move these electrons. Objects at electrostatic equilibrium have no further motion of charge about the surface.The lines extend from this surface outward, not inward. This of course presumes that our conductor does not surround a region of space where there was another charge. When drawing electric field lines, the lines would be drawn from the inner surface of the outer cylinder to the outer surface of the inner cylinder. Any closed, conducting surface can serve as a Faraday's cage, shielding whatever it surrounds from the potentially damaging affects of electric fields, this principle of shielding. This is why we cover delicates in metal boxes. A second characteristic of conductors at electrostatic equilibrium is that the electric field upon the surface of the conductor is directed entirely perpendicular to the surface. If a charge is set into motion, then the object upon which it is on is not in a state of electrostatic equilibrium. The electric field must be entirely perpendicular to the conducting surface for objects that are at electrostatic equilibrium. Certainly a conducting object that has recently acquired an excess charge has a component of electric field (and electric force) parallel to the surface. Once reached, there is no longer any parallel component of electric field.The electric fields are strongest at locations along the surface where the object is most curved. In the end, a relatively large quantity of charge accumulates on the locations of greatest curvature.
Lightning The precursor of any lightning strike is the polarization of positive and negative charges within a storm cloud. The tops of the storm clouds are known to acquire an excess of positive charge and the bottoms of the storm clouds acquire an excess of negative charge. One mechanism involves a separation of charge by a process that bears resemblance to frictional charging.The second mechanism that contributes to the polarization of a storm cloud involves a freezing process. The clouds become further polarized. A storm cloud becomes polarized with positive charges carried to the upper portions of the clouds and negative portions gravitating towards the bottom of the clouds. The air surrounding a cloud would be a good enough insulator to prevent a discharge of electrons to EarthThe insulating air is transformed into a conductive plasma. The ability of a storm cloud's electric fields to transform air into a conductor makes charge transfer from the cloud to the ground possible. A lightning bolt begins with the development of a step leader. As the electrons of the step leader approach the Earth, there is an additional repulsion of electrons.The quantity of positive charge residing on the Earth's surface becomes even greater. This upward rising positive charge - known as a streamer. Once contact is made between the streamer and the leader, a complete conducting pathway is mapped out and the lightning begins. The expansion of the air creates a shockwave that we observe as thunder. Tall buildings, farmhouses and other structures susceptible to lightning strikes are often equipped with lightning rods. The rod serves to prevent a charged cloud from releasing a bolt of lightning. Second, the lightning rod serves to safely divert the lightning to the ground. Lightning dissipation theory, according to the theory, the use of a lightning rod on a building protects the building by preventing the lightning strike. The idea is based upon the principle that the electric field strength is great around a pointed object. Thus preventing the excessive charge buildup that is characteristic of a lightning strike.The lightning diversion theory states that a lighting rod protects a building by providing a conductive pathway of the charge to the Earth. A lightning rod is typically attached by a thick copper cable to a grounding rod that is buried in the Earth below. Lightning researchers are now generally convinced that the lightning dissipation theory provides an inaccurate model of how lightning rods work. There are currently no scientifically verified methods of lightning prevention.
Problems (p. 368 22, 17, 19)
Guiding Questions 10-15
10. What is an electric field? the force exerted on other electrically charged objects by the electrically charged particle the field is surrounding.
11. What are the characteristics and properties of an electric field? See applet: http://www.gel.ulaval.ca/~mbusque/elec/main_e.html An electric charge creates an electric field in the space surrounding it. When a second charged particle approaches the first, it reacts with it, indirectly, through the fields created by both particles.
12. What are the “players” involved in an electric field? The source field, experience field, distance between atoms.
13. What are electric field lines? Direction positive charges are attracted or repelled by negative charges.
14. What are 4 characteristics of electric field lines? 1. Lines go from positive to negative; infinity to negative, or positive to infinity. never negative to anything.2. Lines will never intersect.3. Bigger object, more forceful the lines.4. Perpendicular to emitting source. 15. Go to http://www.physicsclassroom.com/Class/estatics/u8l4c.cfm. Scroll to the bottom of the page and do the “Check Your Understanding” questions.
Electric Field Notes 9/16/11
Region where the space around a charge where another charge will feel an electro static force
The bigger experiencing charge the less influence a source can have on it.
Electric field strength= electric force/ experiencing change
Newtons/ Coloumbs
Electric field are pretty large
Four Characteristics
1. Cant Intersect
2. Out of positive and into the negative
3. More lines the stronger the field
4. The lines come out perpendicular to the service
Table of Contents
Guiding Questions 1-3
1. What is the structure and properties of an atom?An atom consists of a nucleus and a vast region of space outside the nucleus. Nucleus is dense. Electrons are present in the region of space outside the nucleus. They are negatively charged and weakly bound to the atom. Electrons are often removed from and added to an atom by normal everyday occurrences. The nucleus of the atom contains positively charged protons and neutral neutrons . Proton- in nucleus, tightly bound, positive charge, and massive. Neutron- in nucleus, tightly bound, no charge, and massive. Electron- outside nucleus, weakly bound, negative charge, not big.
Ion- charged ion
Anion- negative
Cation- positive
Electronegativity- how tight its bound.
2. What is the symbol and unit of electric charge?
Kind of charge (Q, q)
Unit of charge- Coulombs (C)
e=-1.6 x 10 ^-19 C- charge in a single electron
p=+1.6x 10 ^-19 C- charge in a single proton
Units are usually μC and nC
3. Distinguish between positive and negative charges in as many ways as possible.
Negative charges-
-electrons
- 9.11 x 10^-31 Kg
-mobile
Positive Charges-
Ions- much bigger than single electrons
- more than 10,000 times more massive than electron
- immobile
Problems (1-4)
1. What is the charge on a rod that has 15 excess electrons?2. What is the charge on a pith ball that has 3.15 x 1016 electrons?
3. How many electrons are missing from a balloon that has a charge of 4.19 x 10-5 C?
4. If a metal object receives a positive charge, does its mass increase, decrease, or stay the same? What happens to its mass if the object receives a negative charge?
Losing electrons missing mass
Mass increases when gaining electrons
Lesson 1 Summary 2A
I understood the section on Charge as a Quantity which was very similar to the class discussion. It made sense in the reading that Coulumbs measures the amount of charge an object possesses.Under neutral vs charged objects I was able to make the idea of charged objects clearer in my head. Seeing them gain or lose electrons.
What are the processes of polarization?Polarization- take something charged and touch something neutral. Pushes same charges (neg or pos) to opposite side. Does not change pos. or neg. count by causes a charge.
We really did not go over conductors and insulatorsInsulators dont allow electrons to move easily
Conductors allow electrons to move easily- mostly metals
Guiding Questions 4-9
4. Describe the properties of electric forces.Electric Force: non contact force
Any object can exert this force
Same laws apply to electric force as others
Opposites attract and same repel
5. Distinguish between insulators and conductors.
Conductors are materials that permit electrons to flow freely from atom to atom and molecule to molecule. Insulators are materials that impede the free flow of electrons from atom to atom and molecule to molecule. If charge is transferred to an insulator at a given location, the excess charge will remain at the initial location of charging. The particles of the insulator do not permit the free flow of electrons
6. What is polarization?
Polarization is the process of separating opposite charges within an object. The positive charge becomes separated from the negative charge. By inducing the movement of electrons within an object, one side of the object is left with an excess of positive charge and the other side of the object is left with an excess of negative charge. Charge becomes separated into opposites. Process always involves the use of a charged object to induce electron movement
7. How does a neutral object acquire charge?
A neutral object will acquire a charge by losing or adding protons
8. Distinguish between the 3 charging processes.
Charging by friction: electron affinity- the property of electron affinity refers to the relative amount of love that a material has for electrons- willingness to add electrons- transferred electrons after being rubbed together.
Charging by induction
Charging by conduction- involves conduct
9. What is the law of electric charge?
The interaction between charged objects is a non-contact force that acts over some distance of separation.
Methods of Charging
PolarizationConduction/ Contact- same charge as charging object after being touched by it. move over during polarization than electrons move once being touched.
Induction- start out with a neutral object- bring over a negative rod to start- object becomes polarized- grounding sphere (attached to ground- aground) Electrons leave and go down to ground. When detach grounding wire object is positive
Acquires opposite charge from charging object
Lesson 2 Summary 2A
1. What (specifically) did you read that you already understood well from our class discussion? Describe at least 2 items fully.Charging by friction made a lot of sense to me. Two objects are rubbed together and one has a greater attraction for electrons than the other. When they are rubbed, the one that has a greater attraction receives electrons from the other object. This object now has a negative charge with excess electrons. The other object lost a lot of electrons and now has a positive charge. I understood well how to charge by conduction using a negatively charged object. A negatively charged object makes contact with a neutral object. Since the electrons inside the negatively charged object repel, many of them flow into the neutrally charged object upon contact. This makes the once neutral object have a negative charge.
2. What (specifically) did you read that you were a little confused/unclear/shaky about from class, but the reading helped to clarify? Describe the misconception you were having as well as your new understanding.
The grounding section was explained well. I understand now that when a person touches a charged object, the object becomes neutral.
3.What (specifically) did you read that you still don’t understand? Please word these in the form of a question.
Whats pathway?
4. What (specifically) did you read that was not gone over during class today?
We did not really go over charging by induction
Sticky Lab
Discussion Questions:
In this case, when materials are rubbed against each other, electrons are shed. The object with a greater affinity for electrons will take the electrons that are shed by the other object. Now this object is negative and the other is positive.
This occurs because you are creating friction between your hand and a cat's fur. When this occurs, static electricity builds up and creates a positive charge on one object and a negative on the other. The sound and sparks that result from this are the electrons moving from the negative object to the positive one.
Copy machines work by using a process known as xerography. They have a a special film known as a photoreceptor, which when charged, can erase a charge by shining light upon it. When copying, the machine's electricity causes the air to form positive charges, which are spread onto the photoreceptor. A beam of light is then used to write on the photoreceptor; the location of the writing depends on the original paper placed into the copier. Toner, which has a negative charge, is then shaken over the sheet and sticks to the positive charges left on the photoreceptor. The piece of paper is then pressed onto the photoreceptor, which, in turn, presses the content from the original piece of paper onto the copying paper.
PVC(++), Wool (+++++), Styrene (++++), Teflon (+), Polyester (+++)
Accepts Most Electrons to Gives away the most
1. Teflon
2. PVC
3. Polyester
4. Styrene
5. Wool
PVC will accept from wool
Teflon accepts electrons from the PVC
PVC accepts the electrons of the Polyester
Teflon accepts the electrons of the Polyester
Styrene accepts the electrons from the wool
Conclusion:
Revisit your hypotheses and answer the objectives in light of your observations. Be sure to be specific, supporting your statements with evidence from the lab.
Practice Problems (5-7, 12)
12. Increasing speed
Balloon Activity
Electrostatic Force
The attraction or repulsion between 2 electric chargesFe= (Ke|q1||q2|)/d^2
Charge is in C
Make sure not micro Coulombs
Distance in meters
Force in newtons
Exert equal and opposite forces on 1st.
Ke= 9x10^9 Nm^2/c^2
Electrostatic can attract and repel but gravitational can only attract
Putting two positively charged together you get increasing motion
Positive and Negative increasing motion
Lesson 3 Summary 2A
Electric Fields
Lesson 4 Summary Method 1
Action at a distanceThe electric force acts over the distance separating the two objects. Electric force is an action-at-a-distance force. There are two categories of forces - contact forces and non-contact forces. The charged object affects other charged objects that were in the surrounding neighborhood. The best explanation to this question involves the introduction of the concept of electric field. The concept of a field force is utilized by scientists to explain this. While all masses attract when held some distance apart, charges can either repel or attract when held some distance apart. A charged object creates an electric field. A Van de Graaff generator is a large conducting sphere that acquires a charge as electrons are scuffed off of a rotating belt. The Van de Graaff generator is said to create an electric field in the space surrounding it. An electric charge creates an electric field and as masses get near it, it will have a stronger effect.
Electric Field Intensity
Electric field strength is a vector quantity; it has both magnitude and direction. The magnitude of the electric field strength is defined in terms of how it is measured.The strength of the source charge's electric field could be measured by any other charge placed somewhere in its surroundings. The charge that is used to measure the electric field strength is referred to as a test charge. The magnitude of the electric field is simply defined as the force per charge on the test charge. Since electric field is defined as a force per charge, the standard metric units are Newton/Coulomb or N/C. The electric field strength is not dependent upon the quantity of charge on the test charge. The electric field strength is not dependent upon the quantity of charge on the test charge. Coulomb's law states that the electric force between two charges is directly proportional to the product of their charges and inversely proportional to the square of the distance between their centers. E =F/q equation. The electric field strength is dependent upon the quantity of charge on the source charge (Q) and the distance of separation (d) from the source charge. The electric field strength formula illustrates an inverse square relationship between electric field strength and distance, known as an inverse square law. Electric field strength is location dependent, and its magnitude decreases as the distance from a location to the source increases. Every electric charge creates an electric field. The strength of a source charge's electric field is dependent upon how charged up the source charge is. The electric field equation shows that as you get closer and closer to the source of the field, the affect becomes greater and greater, the electric field strength increases. The magnitude of the electric field vector is calculated as the force per charge on any given test charge located within the electric field. The precise direction of the force is dependent upon whether the test charge and the source charge have the same type of charge. A positive test charge is pushed or pulled when in the presence of the electric field. Electric field vectors are always directed towards negatively charged objects.
Electric Field Lines
Electric field lines point in the direction that a positive test charge would accelerate if placed upon the line. As such, the lines are directed away from positively charged source charges and toward negatively charged source charges. One common convention is to surround more charged objects by more lines. Objects with greater charge create stronger electric fields. Not only does the density of lines surrounding any given object reveal information about the quantity of charge on the source charge, the density of lines at a specific location in space reveals information about the strength of the field at that location. A second rule for drawing electric field lines involves drawing the lines of force perpendicular to the surfaces of objects at the locations where the lines connect to object's surfaces.A final rule for drawing electric field lines involves the intersection of lines. Electric field lines should never cross. Suppose that there are two positive charges - charge A (QA) and charge B (QB) - in a given region of space. Each charge creates its own electric field. Since electric field is a vector, the usual operations that apply to vectors can be applied to electric field. That is, they can be added in head-to-tail fashion to determine the resultant or net electric field vector at each location. Ultimately, the electric field lines surrounding the configuration of our two charges would begin to emerge. For the limited number of points selected in this location, the beginnings of the electric field line pattern can be seen.
Electric Fields and Conductors
Electrostatic equilibrium is the condition established by charged conductors in which the excess charge has optimally distanced itself so as to reduce the total amount of repulsive forces. There is no further motion of charge about the surface after this equilibrium. One characteristic of a conductor at electrostatic equilibrium is that the electric field anywhere beneath the surface of a charged conductor is zero. If an electric field did exist beneath the surface of a conductor, then the electric field would exert a force on all electrons that were present there. This net force would begin to accelerate and move these electrons. Objects at electrostatic equilibrium have no further motion of charge about the surface.The lines extend from this surface outward, not inward. This of course presumes that our conductor does not surround a region of space where there was another charge. When drawing electric field lines, the lines would be drawn from the inner surface of the outer cylinder to the outer surface of the inner cylinder. Any closed, conducting surface can serve as a Faraday's cage, shielding whatever it surrounds from the potentially damaging affects of electric fields, this principle of shielding. This is why we cover delicates in metal boxes. A second characteristic of conductors at electrostatic equilibrium is that the electric field upon the surface of the conductor is directed entirely perpendicular to the surface. If a charge is set into motion, then the object upon which it is on is not in a state of electrostatic equilibrium. The electric field must be entirely perpendicular to the conducting surface for objects that are at electrostatic equilibrium. Certainly a conducting object that has recently acquired an excess charge has a component of electric field (and electric force) parallel to the surface. Once reached, there is no longer any parallel component of electric field.The electric fields are strongest at locations along the surface where the object is most curved. In the end, a relatively large quantity of charge accumulates on the locations of greatest curvature.
Lightning
The precursor of any lightning strike is the polarization of positive and negative charges within a storm cloud. The tops of the storm clouds are known to acquire an excess of positive charge and the bottoms of the storm clouds acquire an excess of negative charge. One mechanism involves a separation of charge by a process that bears resemblance to frictional charging.The second mechanism that contributes to the polarization of a storm cloud involves a freezing process. The clouds become further polarized. A storm cloud becomes polarized with positive charges carried to the upper portions of the clouds and negative portions gravitating towards the bottom of the clouds. The air surrounding a cloud would be a good enough insulator to prevent a discharge of electrons to EarthThe insulating air is transformed into a conductive plasma. The ability of a storm cloud's electric fields to transform air into a conductor makes charge transfer from the cloud to the ground possible. A lightning bolt begins with the development of a step leader. As the electrons of the step leader approach the Earth, there is an additional repulsion of electrons.The quantity of positive charge residing on the Earth's surface becomes even greater. This upward rising positive charge - known as a streamer. Once contact is made between the streamer and the leader, a complete conducting pathway is mapped out and the lightning begins. The expansion of the air creates a shockwave that we observe as thunder. Tall buildings, farmhouses and other structures susceptible to lightning strikes are often equipped with lightning rods. The rod serves to prevent a charged cloud from releasing a bolt of lightning. Second, the lightning rod serves to safely divert the lightning to the ground. Lightning dissipation theory, according to the theory, the use of a lightning rod on a building protects the building by preventing the lightning strike. The idea is based upon the principle that the electric field strength is great around a pointed object. Thus preventing the excessive charge buildup that is characteristic of a lightning strike.The lightning diversion theory states that a lighting rod protects a building by providing a conductive pathway of the charge to the Earth. A lightning rod is typically attached by a thick copper cable to a grounding rod that is buried in the Earth below. Lightning researchers are now generally convinced that the lightning dissipation theory provides an inaccurate model of how lightning rods work. There are currently no scientifically verified methods of lightning prevention.
Problems (p. 368 22, 17, 19)
Guiding Questions 10-15
10. What is an electric field?the force exerted on other electrically charged objects by the electrically charged particle the field is surrounding.
11. What are the characteristics and properties of an electric field? See applet: http://www.gel.ulaval.ca/~mbusque/elec/main_e.html
An electric charge creates an electric field in the space surrounding it. When a second charged particle approaches the first, it reacts with it, indirectly, through the fields created by both particles.
12. What are the “players” involved in an electric field?
The source field, experience field, distance between atoms.
13. What are electric field lines?
Direction positive charges are attracted or repelled by negative charges.
14. What are 4 characteristics of electric field lines?
1. Lines go from positive to negative; infinity to negative, or positive to infinity. never negative to anything.2. Lines will never intersect.3. Bigger object, more forceful the lines.4. Perpendicular to emitting source.
15. Go to http://www.physicsclassroom.com/Class/estatics/u8l4c.cfm. Scroll to the bottom of the page and do the “Check Your Understanding” questions.
Electric Field Notes 9/16/11
Region where the space around a charge where another charge will feel an electro static forceThe bigger experiencing charge the less influence a source can have on it.
Electric field strength= electric force/ experiencing change
Newtons/ Coloumbs
Electric field are pretty large
Four Characteristics
1. Cant Intersect
2. Out of positive and into the negative
3. More lines the stronger the field
4. The lines come out perpendicular to the service
Concept Map